The in-vitro susceptibilities of 40 clinical isolates of Candida albicans to ketoconazole and fluconazole were determined and an attempt was made to correlate these data with the clinical responses of the patients from whom the strains were originally isolated to treatment with these agents. Of 40 patients with the acquired immunodeficiency syndrome (AIDS) with oropharyngeal and/or oesophageal candidosis, 21 received ketoconazole and 19 fluconazole. Susceptibility testing was performed by a microbroth dilution method with RPMI-2% glucose medium according to the recommendations of the National Committee for Clinical Laboratory Standards; growth inhibition was estimated spectrophotometrically and the MIC endpoint was defined in terms of the IC1/2. The MICs of 236 additional strains of C. albicans, which were also isolated from AIDS patients, were used to establish a susceptibility profile for this species. On the basis of the susceptibility test results and the clinical responses of the 40 patients, the following tentative breakpoints for ketoconazole and fluconazole are proposed: patients with infections caused by C. albicans strains with MICs of ketoconazole and fluconazole or < or = 0.001 and < or = 0.25 mg/L respectively would be expected to respond to treatment with these agents and isolates with MICs which meet these criteria are therefore classified as susceptible; patients with infections caused by strains with MICs of ketoconazole and fluconazole of > or = 0.06 and > or = 16.0 mg/L respectively would not be expected to respond to treatment with these agents and isolates with MICs which meet these criteria are therefore classified as resistant; the response of patients with infections caused by strains with MICs of ketoconazole and fluconazole of 0.003-0.03 and 0.5-8.0 mg/L respectively cannot be reliably predicted and isolates with MICs which fall within these ranges are therefore classified as being of indeterminate susceptibility. The present study demonstrates that the results of in-vitro susceptibility testing with RPMI-2% glucose broth correlate with the clinical response to therapy and can be used to facilitate optimal treatment in AIDS patients with oropharyngeal and/or oesophageal candidosis.